Method of manufacturing plug-in electrical fuses

ABSTRACT

A plug-in electrical fuse comprises a fusible wire (9) disposed within an insulating housing (1) and connected between the ends of two blade-like terminals (4) secured within and projecting from the housing. Fuses of this type are manufactured by forming a strip of terminal members from strip metal, each member comprising two spaced substantially-coplanar blade-like terminal portions interconnected at their leading ends (5) by an integral cross-bar portion, and each terminal member being integrally connected with each adjacent terminal member in the strip by an interconnecting bar of the metal strip. Fusible wire is secured to the terminal portions adjacent their rear ends to form a strip of terminal and wire assemblies, and this strip of assemblies is mounted in a strip of insulating housings with the fusible wires disposed within the housings and the leading ends of the terminal portions projecting therefrom. The interconnecting and cross-bar portions between adjacent assemblies and between the terminal portions of each assembly are then severed so as to separate the strip into individual fuses. The housings may be retained connected together in strip form and be separated only when the fuses are required for use.

BACKGROUND OF THE INVENTION

The present invention relates to plug-in electrical fuses of the typedesigned to be plugged directly into socket openings which extendtransversely to the length of the fuse body. Such fuses are especiallysuitable for use in protecting automobile electrical circuits.

A typical plug-in fuse of the above type is described in British PatentSpecification No. 1,500,183. This fuse includes a fuse element in theform of a one-piece, plate-like body of fuse metal, the body comprisinga pair of laterally spaced generally parallel terminals, each of whichcomprises a blade portion adapted, in use, to be inserted into a socket,such as a pressure clip terminal, in a mounting panel, and a fusiblelink portion, of smaller cross-sectional area than the blade terminals,integral with the terminals at positions remote from their leading ends.The fuse element is mounted in an insulating housing so that the fusiblelink portion is enclosed in the housing and the leading ends of theblade terminals project therefrom for plugging into cooperating sockets.Such fuse elements may readily be mass-produced by stamping them fromthe end of a strip of fuse metal, preferably, after selected areas havebeen milled and/or compressed to reduce the cross-sectional areas of theportions of the strip which are to constitute the fusible link portionsof the fuse elements.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an improved method ofmanufacturing plug-in fuses of the type referred to which facilitatesmass production of such fuses. The improved method also results in anovel construction of plug-in fuse which is interchangeable with otherknown fuses of this type.

From one aspect, the present invention is directed to a method of makinga plug-in electrical fuse of the type referred to, which methodcomprises the steps of forming a terminal member from sheet metalmaterial, which member has two spaced, substantially coplanar,blade-like terminal portions interconnected at or adjacent leading endsby an integral cross-bar portion, securing a fusible element to theterminal portions at or adjacent rear ends thereof, mounting theresulting assembly in an insulating housing with the fusible elementdisposed within the housing and the leading ends of the terminalportions projecting therefrom, and severing the cross bar from theterminal portions.

The terminal member may be formed as a simple stamping from sheet metalmaterial. However, accordingly to a preferred embodiment, it is formedby stamping a generally H-shaped blank from the sheet material, foldingthe blank about an axis substantially parallel to the cross bar of theH-shape so as to dispose upper and lower portions of the uprights of the"H" in mutually opposed relation to form two blade-like terminalportions of double laminar construction. The laminar forming each of theterminal portions are integrally joined at the leading ends of theterminals, and the terminal portions remain joined together by thecross-bar of the original H-shape until this cross-bar is severed at alater stage in the production of the fuse.

The fusible element, which may comprise a length of fusible wire, may besoldered or welded to the terminal portions adjacent the rear endsthereof. To permit the length of the fusible link provided by the fuseelement to be maximized, the terminal portions may be formed, at theirrear ends, with mutually opposed rebates, and the fuse element may beconnected between the remaining, rearwardly projecting lugs of theterminals. These rearwardly projecting lugs may be engaged in openingsextending through the adjacent wall of the insulating housing so as tobe accessible through the wall of the housing. Such a constructionaffords the terminals increased stability and permits testing of acircuit in which the fuse is connected without removal of the fuse.

In the preferred embodiment, where the terminal member is formed from afolded, H-shaped blank so that the blade-like terminal portions have adouble laminar construction, the fuse element may be held or clampedbetween the opposed laminar portions of each terminal, which are foldedand flattened with the element disposed therebetween, whereafter theelement may be soldered or welded in position. For this purpose, thesheet material from which the terminal blank is formed may be tinned orsolder coated and the fusible element may have blobs of solder attachedthereto at appropriate positions. Soldering of the fusible elementbetween the laminar portions is then accomplished by the application ofheat and pressure. Alternatively, when the fusible element is notprovided with solder blobs, the terminal and fusible element assemblymay be dip soldered to secure the wire in position.

For higher current ratings, which would require a fuse wire ofrelatively large diameter, it may be desirable to use a rolled,flattened fusible wire, thereby to reduce the bulk of the fuse wiredisposed between the laminar portions of the terminals and permit thelaminar portions to be satisfactorily flattened together into abuttingrelation. Alternatively, to permit the laminar portions to be completelyflattened together with a fusible element therebetween, one or both ofthe laminar portions may be formed with an inwardly facing transversegroove at the position where the fusible element is to be secured. Bysolder dipping, the groove may be filled with solder before positioningof the fusible element, which would not require solder blobs at itsfixing positions. The application of heat and pressure closes thelaminar portions together and secures the element in the groove(s). Thismethod of securing the fusible element may also be used where theterminal member comprises a single lamination and is formed as a simplestamping from sheet material. In this case, transverse grooves areformed respectively in corresponding faces of the blade-like terminalportions, at the positions where the fusible element is to be fixed, andthese grooves are filled with solder by dip soldering and the fusibleelement is secured in the grooves by the application of heat andpressure.

The insulating housing may have a slot-like cavity extending thereintofrom one edge of the housing for receiving the rear ends of the bladeterminals and the fusible element. The terminal and element assembly maybe secured in the housing by means of dimples or detents formed in theterminal portions which snap into engagement with cooperating detents ordimples formed in the cavity walls when the assembly is inserted intothe housing cavity. In one embodiment, the transverse grooves formed inthe terminal portion for the purposes of locating and fixing the fusibleelement may form transverse ribs on the outsides of the terminals whichserve as detents and snap into cooperating dimples in the cavity wallsto secure the terminals in position.

The present invention is particularly adapted to enable the manufactureof plug-in fuses by mass production techniques. Hence, from anotheraspect, the invention is directed to a method of mass-producing plug-inelectrical fuses of the type referred to, which method comprises thesteps of forming a strip of terminal members from sheet metal material,each member having two spaced, substantially coplanar, blade-liketerminal portions interconnected at or adjacent leading ends by anintegral cross-bar portion, and each member being integrally connectedwith the or each adjacent terminal member in the strip by aninterconnecting bar of the sheet material, securing a fusible element orelements to the terminal portions at or adjacent rear ends thereof toform a strip of terminal and element assemblies, mounting the assembliesin insulating housings with the fusible elements disposed within thehousings and the leading ends of the terminal portions projectingtherefrom, and severing the interconnecting and cross-bar portions ofsheet material from between adjacent assemblies and from between theterminal portions of each assembly so as to separate the strip intoindividual fuses.

The strip of terminal members may be a simple stamping from strip metalmaterial or in accordance with the preferred embodiment may be stampedas a strip of H-shaped terminal blanks, each of which is integral withthe or each adjacent blank in the strip via an interconnecting bar ofthe sheet material extending substantially parallel to the cross-bars ofthe H-shaped blanks. In the latter event, the strip of H-shaped blanksis folded about an axis substantially parallel to the cross-bars of theH-shapes so as to dispose upper and lower laminar portions of theuprights of each H-shape in mutually opposed relation for forming thetwo blade-like terminal portions of double laminar construction for eachfuse.

Conveniently, adjacent terminal blanks in the strip are spaced from oneanother, by the interconnecting bars, by the same distance as thespacing between the terminal portions of each blank, and theseinterconnecting bars are disposed coaxially with the cross-bar portionsof the terminal blanks. The fusible element may be formed from a fusewire which is of sufficient length to be secured to the terminalportions of all the blanks in the strip. If this fuse wire is welded orsoldered with the aid of blobs of solder previously attached to thewire, in the manner described above, the solder blobs are attached tothe wire at intervals corresponding to the spacing between adjacentterminal portions.

From a further aspect, the present invention is directed to a novelconstruction of plug-in electrical fuse of the type comprising aninsulating housing, a pair of substantially coplanar, blade-liketerminals projecting from the housing substantially parallel to oneanother, and a fusible element secured between the blade terminalswithin the housing.

In the preferred embodiment, each blade-like terminal comprises twolaminar portions disposed in mutually opposed abutting relation andintegrally joined at the projecting or leading end of the terminal.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that the present invention may be more readily understood,reference will now be made to the accompanying drawings, in which:

FIG. 1 is a side elevation of a plug-in electrical fuse constructed inaccordance with the invention,

FIG. 2 is a section on the line II--II of FIG. 1,

FIG. 3 is a plan view of a strip of terminal blanks used in themanufacture of plug-in fuses the type illustrated in FIGS. 1 and 2,

FIGS. 4, 5 and 6 illustrate steps in the method of manufacturing suchfuses,

FIGS. 7, 8 and 9 illustrate the method of manufacturing anotherembodiment of the invention, and

FIGS. 10 and 11 illustrate the method of manufacturing a furtherembodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIGS. 1 and 2, the plug-in electrical fuse comprises agenerally rectangular housing 1 made from insulating material, such as aplastics material, and having a slot-like cavity 2 extending into thehousing from the bottom edge thereof. The housing has small shoulders 3moulded at opposite ends thereof for facilitating plugging-in andremoval of the fuse. A pair of substantially coplanar, blade-liketerminals 4 are mounted within the slot-like cavity 2 of the housing insubstantially parallel relation and have leading ends 5 projecting fromthe housing. The rear ends of the terminals are formed with mutuallyopposed rebates 6 and the remaining, rearwardly-projecting lugs 7 areengaged in openings 8 extending through the adjacent, top wall of thehousing 1 so that electrical contact can be made with the terminals, ifdesired, for example, for the purposes of circuit testing withoutnecessitating removal of the fuse. Each terminal 4 is composed of twolaminar portions 10a, 10b disposed in mutually opposed, abuttingrelation and integrally joined together at the leading end 5 of theterminal, about which these laminar portions are folded to produce theterminal, as will hereinafter be more fully described. During themanufacturing process, the laminar portions 10a,10b of each terminal areflattened together and a fusible wire 9, which extends between the lugs7 adjacent the rear wall of the slot 2 is secured to each terminal bybeing clamped and soldered between the flattened laminar portions10a,10b. The terminals are retained in position in the housing bydetents 11 on the outside surfaces of the laminar portions 10a,10b whichsnap into engagement with cooperating dimples 12 on the opposing insidesurfaces of the slot-like cavity 2.

Fuses of the construction described with reference to FIGS. 1 and 2 maybe mass-produced as follows. Referring to FIG. 3, a continuous strip ofterminal blanks 13 is stamped from sheet metal strip. Each blank 13 isof generally H-shape in plan and comprises upright laminar portions 14,which have mutually opposed rebates 15 at opposite ends, and a centralcross-bar 16. Adjacent blanks in the strip are joined together byinterconnecting bars 17 of the strip material which are coaxial with andidentical of the cross-bars 16. To facilitate folding of the strip aboutthe central longitudinal axis A--A of the bars 16,17, elongated openings18 are formed centrally of the bars during the stamping process. Also,during the stamping process, the small detents 11, such as tags, areformed in the upper and lower portions 10a,10b of the uprights 14 so asto project from one side of the strip.

Following stamping, the strip of terminal blanks 13 is foldedlongitudinally about the axis A--A so as to dispose the upper and lowerlaminar portions 10a,10b of the uprights 14 in mutually opposed relationfor forming the blade-like terminals 4 of the fuses. The detents 11 aredisposed on the outsides of the folded strips. As shown in FIG. 4, thestrip is initially folded only to a partially closed position, whereupona continuous length of fusible wire 19 having blobs 20 of solderattached thereto at intervals corresponding to the spacing betweenadjacent terminals is located between the partially folded laminarportions 10a,10b adjacent their ends remote from the fold, that is,between the projecting lug portions 21 formed by the rebates 15 andwhich constitute the lugs 7 in the finished fuses. The opposing laminarportions 10a, 10b are then flattened together into abuttingrelationship, as shown in FIGS. 5 and 6, in order to produce terminalmembers having blade-like terminals 4 and clamp and hold the fuse wire19, and the wire is soldered in position by the application of heat andpressure. The terminal blanks 13 are tinned or solder coated prior tothe folding process in order to permit this soldering operation.

Having severed the continuous fuse wire 19 at locations between adjacentterminal members or pairs of terminals so as to leave the pairs ofterminals electrically connected by the fuse wire links 9, the resultingstrip of terminal and fuse wire assemblies are attached to insulatinghousings 1. The latter are moulded in "chocolate block" form and arefitted to the terminal and fuse wire assemblies as a strip of housingsinterconnected by thin webs of the plastics insulating material. Thesewebs space the housings at intervals corresponding to the spacingbetween the terminal and wire assemblies of the terminal strip. The rearends (see FIGS. 1 and 2) of the pair of terminals 4 of each assembly areinserted into the slot-like cavity 2 of an associated housing and thelugs 7 engage in the openings 8 in the rear wall of the housing whilstthe detents 11 on the outside faces of the terminals snap intoengagement with the cooperating dimples 12 moulded on the insidesurfaces of the slot-like cavity so as to mount and retain theterminals, together with the associated fuse wire link 9, in thehousing. After assembling the terminals to the housings, theinterconnecting bars 17 of strip material (see FIG. 5) between adjacentassemblies, and the cross-bars 16 between the terminals of each assemblyare cropped out in order to separate the terminal strip into individualfuses. However, the fuses may be retained connected together in stripform by the plastics webs interconnecting the housings and these may bebroken to separate the fuses only when they are required for use.

FIGS. 7, 8 and 9 illustrate a modified method of fixing the fusiblewire, whereby the wire fixing arrangement also serves as detents forsecuring the terminals within the insulating housing. Hence, theprojecting lugs 21 at opposite ends of the uprights 14 are formed withtransverse grooves 22 which, when the upper and lower laminar portions10a,10b of the uprights are folded into opposing relation, arethemselves disposed in opposing relation on the insides of the portionsand in alignment with the grooves in the associated laminar portions.Prior to folding, the grooves are filled with solder by a solder dippingprocess and, after the strip is folded to its partially closed positionshown in FIG. 7, a continuous fusible wire 23, without solder blobs, islocated between the partially folded portions in register with thegrooves, and then the laminar portions 10a,10b are flattened togetherwith the application of pressure and heat so that the wire is solderedin position within the grooves 22 and the laminar portions are fullyflattened together (FIGS. 8 and 9). The grooves 22 form ribs 24 on theoutsides of the laminar portions and are so shaped that these ribs aregenerally barb-like in cross section, with the barbs facing towards theformed, leading ends 5 of the laminar portions. These barb-like ribs 24serve as detects to secure the terminals within the slot-like cavity 2in the housing 1 and, when a terminal assembly is inserted into theslot-like cavity in its associated housing, the ribs 24 snap intocooperating grooves 25 in the inside surfaces of the cavity when theassembly is fully inserted (FIG. 9).

FIGS. 10 and 11 illustrate the manufacturing of plug-in electrical fusesin which the blade-like terminals consist of a single thickness of sheetmetal. A continuous strip of terminal members 26 is blanked or stampedfrom sheet metal strip. Each member or blank 26 comprises two spaced,blade-like terminal portions 27 interconnected by an integral cross-barportion 28 adjacent the leading ends 29 of the terminals. Adjacentmembers in the strip are joined together by interconnecting bars 30 ofthe strip material which are coaxial with and identical to the cross-barportions 28. At their rear ends, each pair of terminal portions 27 isformed with mutually opposed rebates 31 so as to leave rearwardlyprojecting lugs 32. During the stamping process, these lugs are formedin corresponding faces with aligned grooves 33 which define a projectingrib 34 on the opposite face of barb-like configuration. The lugs 32 aresolder-dipped to fill the grooves 33 with solder and, thereafter, acontinuous length of fusible wire 35 is located along the grooves and issoldered in position in the grooves by the application of pressure andheat. The wire 35 is then severed, the strip of terminal and fuse wireassemblies is mounted in a strip of insulating housings (not shown)similar to those of the previous embodiments and the interconnectingbars 30 of strip material between adjacent assemblies and the cross-barportions 28 between the terminal portions 27 of each assembly aresevered in order to separate the strip into individual fuses. Theterminals are retained in the insulating housings by the ribs 34 whichsnap into engagement with cooperating grooves moulded on the insidesurfaces of the slot-like cavities in the housings.

Whilst particular embodiments have been described, it will be understoodthat various modifications can be made without departing from the scopeof the invention. For example, where a short fusible link is acceptable,rebates 6 need not be formed at the rear ends of the blade-liketerminals in the region where the fusible wire is to be secured and thewire may simply be secured between the main bodies of the terminals.

I claim:
 1. A method of manufacturing a plug-in electrical fuse of thetype in which the fusible element is disposed within an insulatinghousing and is electrically connected between the adjacent ends of twospaced substantially-coplanar blade-like terminals secured within andprojecting from the housing comprising the steps of:forming a generallyH-shaped terminal blank from sheet metal material, said blank havinglaminar uprights integrally joined by a laminar cross-bar portion,folding said H-shaped blank about an axis substantially parallel to saidcross-bar portion of said blank to dispose upper and lower laminarportions of said uprights of said H-shaped blank in generally mutuallyopposed relationship, locating a fusible element so that it is disposedbetween the opposed laminar portions of said blank, flattening saidopposed laminar portions together with said fusible element disposedtherebetween to form an assembly including blade-like terminal portionsof double laminar construction having said fusible element electricallyconnected therebetween, mounting said assembly in an insulating housingwith said fusible element disposed within said housing and the leadingends of said blade-like terminal portions projecting therefrom, andsevering said cross-bar portion from between said terminal portions. 2.The method claimed in claim 1, in which said sheet material, from whichsaid terminal blank is formed, is tinned and said fusible element hasblobs of solder attached thereto at positions corresponding to saidterminal portions, and in which said fusible element is soldered inposition between said opposed laminar portions of the folded blank byapplying heat and pressure thereto.
 3. The method claimed in claim 1, inwhich the terminal and element assembly is dip-soldered to secured saidfusible element in position.
 4. A method of manufacturing plug-inelectrical fuses of the type in which a fusible element is disposedwithin an insulating housing and is electrically connected between theadjacent ends of two spaced substantially-coplanar blade-like terminalssecured within and projecting from said housing, comprising the stepsof:forming a strip of generally H-shaped terminal blanks from sheetmetal material, each said blank having laminar uprights integrallyjoined by a laminar cross-bar portion and each said blank beingintegrally joined with an adjacent blank in said strip by aninterconnecting bar portion of said sheet material extendingsubstantially parallel to said cross-bar portions of said H-shapedblanks, folding said strip of H-shaped blanks about an axissubstantially parallel to said cross-bar portions of said blanks todispose upper and lower laminar portions of said uprights of each saidH-shaped blank in generally mutually opposed relationship, locating fuseelement means so as to be disposed between the opposed laminar portionsof said blanks, flattening said opposed laminar portions together withsaid fuse element means disposed therebetween and forming a strip ofterminal and element assemblies, each of which includes two blade-liketerminal portions of double laminar construction having a fusibleelement electrically connected therebetween. mounting said assemblies ininsulating housings with said fusible elements disposed within saidhousings and the said leading ends of said terminal portions projectingtherefrom, and severing said interconnecting and cross-bar portions frombetween adjacent assemblies and from between said two terminal portionsof each assembly for separating said strip into individual fuses.
 5. Themethod claim in claim 4, in which said sheet material, from which saidstrip of terminal blanks is formed, is tinned and said fuse elementmeans has blobs of solder attached thereto at positions corresponding tosaid terminal portions, and in which said fuse element means is solderedin position between said opposed laminar portions of the folded blanksby applying heat and pressure thereto.
 6. The method claimed in claim 4,in which said terminal and element assemblies are dip-soldered to securesaid fuse element means in position.
 7. The method claimed in claim 4,in which said fusible element means is soldered to said terminalportions adjacent the rear ends thereof.
 8. The method claimed in claim4, in which adjacent said terminal blanks in said strip are spaced fromone another, by said interconnecting bar portions, by substantially thesame distance as the spacing between said uprights of each of saidblanks, and said interconnecting bars are disposed coaxially withrespect to said cross-bar portions of said terminal blanks.
 9. Themethod claimed in claim 4, including the step of forming at least one ofeach pair of said opposed laminar portions with an inwardly facingtransverse groove at the position where said fuse element means is to besecured.
 10. The method claimed in claim 4, in which each of saidinsulating housings has a slot-like cavity extending thereinto from oneedge of said housing for receiving the rear ends of the associatedterminal and element assembly, and in which each terminal and elementassembly is secured in the associated housing by means of cooperatingdimples and detents formed in said terminal portions and the cavitywall, said dimples and detents snapping into engagement when saidassembly is inserted into the housing cavity.
 11. The method claimed inclaim 10, in which at least one of each pair of said opposed laminarportions is formed with an inwardly facing transverse groove at theposition where said fuse element means is to be secured and in whichsaid transverse grooves form transverse ribs on the outsides of saidterminal portions of each said assembly which serve as said detents andsnap into cooperating dimples in said cavity wall to secure saidassembly in position in said associated housing.
 12. The method claimedin claim 4, in which said terminal portions of each folded blank havemutually opposed rebates at their rear ends, and said fuse element meansis connected between the rearwardly projecting lugs defined by saidrebates.
 13. The method claimed in claim 12, in which said rearwardlyprojecting lugs are engaged in openings extending through an adjacentwall of the associated insulating housing so as to be accessible throughsaid wall of said housing.